An inch is a unit of length equal to 1/12 of a foot or 1/36 of a yard. Because the international yard is legally defined to be equal to exactly 0.9144 meters, one inch is equal to 2.54 centimeters.[2]
The inch is a US customary and imperial unit of length. Inches can be abbreviated as in; for example, 1 inch can be written as 1 in.
Inches can also be denoted using the ″ symbol, otherwise known as a double-prime. Often a double-quote (") is used instead of a double-prime for convenience. A double-prime is commonly used to express 1 in as 1″.
The standard ruler is 12 inches long and is a common tool for measuring a length in inches. Another frequently used tool to perform measurements in inches is a tape measure, which commonly comes in lengths from 6' - 35'. Other types of devices used to make measurements in inches include scales, calipers, measuring wheels, micrometers, yardsticks, and even lasers.
Learn more about inches.
What Is a Millimeter?One millimeter is equal to one-thousandth (1/1,000) of a meter, which is defined as the distance light trels in a vacuum in 1/299,792,458 of a second. One millimeter is equal to 0.0393701 inches.
The millimeter, or millimetre, is a multiple of the meter, which is the SI base unit for length. In the metric system, "milli" is the prefix for thousandths, or 10-3. Millimeters can be abbreviated as mm; for example, 1 millimeter can be written as 1 mm.
Millimeters are often represented by the smallest ticks on most metric rulers. To get a reference point of the size, the thickness of a US dime is 1.35mm.[3]
Learn more about millimeters.